Q: Car idling low at stop

If you have a Check Engine Light, I would start there. Any codes that are found will aid in the diagnosis of your issue. It is possible that you could have an issue with your idle air control valve. I would recommend having your engine inspected by an experienced technician for vacuum leaks and issues with your IAC valve. Since the IAC valve is an electronic part, this could explain why the problem happened suddenly as electrical parts can become inoperative without warning. Once the source of the problem is found, I would recommend having it repaired as soon as you can to prevent any engine damage due to running improperly for a long period of time.